Sensing element and optical distance measurement system

ABSTRACT

A sensing element includes a plurality of sensing pixel areas arranged in matrix, wherein each of the plurality of sensing pixel areas includes a first pixel, a second pixel, a first shielding layer, a second shielding layer and at least one micro lens. The second pixel is adjacent to the first pixel in a predetermined direction. The first shielding layer is disposed on the first pixel and has a first opening, wherein an aperture of the first opening increases along the predetermined direction from a center of the first pixel. The second shielding layer is disposed on the second pixel and has a second opening, wherein a shape of the second opening is mirror symmetrical with that of the first opening in the predetermined direction. The at least one micro lens is disposed on the first shielding layer and the second shielding layer.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan Patent Application Serial Number 104112987, filed on Apr. 22, 2015, the full disclosure of which is incorporated herein by reference.

BACKGROUND 1. Field of the Disclosure

This disclosure generally relates to a sensing element, more particularly, to a sensing element an optical distance measurement system applicable to the distance measurement or the gesture recognition.

2. Description of the Related Art

In general, a distance measurement system employs a light source and calculates an object distance according to energy of light beam of the light source reflected back by the object. Traditionally, it is able to use the triangulation method or time-of-flight (TOF) technique to calculate the distance. However, these methods require a higher cost and a larger system size.

In addition, the development of gesture recognition generally removes the background image at first by using a 3D image so as to separate the object image. In this technique, two image sensors are used such that the size and cost of a gesture recognition module can not be effectively reduced.

As mentioned above, the present disclosure obtains the 3D image by using the phase detection, and an additional illumination light (as used in the TOF mentioned above) is not necessary. In the proposed technique of the present disclosure, a single image sensor is employed to be able to implement the distance measurement and the gesture recognition.

SUMMARY

Accordingly, the present disclosure provides a sensing element and an optical distance measurement system with a low cost, small size and high detection accuracy.

The present disclosure provides an optical distance measurement system including a lens, a sensing element and a processing unit. The sensing element senses light penetrating the lens and outputs an image frame, and includes a plurality of sensing pixel areas arranged in a matrix, wherein each of the sensing pixel areas includes a first pixel, a second pixel, a first shielding layer, a second shielding layer and at least one micro lens. The second pixel is adjacent to the first pixel in a predetermined direction. The first shielding layer is disposed upon the first pixel and has a first opening, wherein an aperture of the first opening increases along the predetermined direction from a center of the first pixel. The second shielding layer is disposed upon the second pixel and has a second opening, wherein a shape of the second opening is mirror symmetrical to that of the first opening along the predetermined direction. The at least one micro lens is disposed between the lens and the first shielding layer as well as the second shielding layer. The processing unit generates, according to the image frame, a first subframe corresponding to the first pixels and a second subframe corresponding to the second pixels, and calculates at least one object distance according to the first subframe and the second subframe.

The present disclosure further provides a sensing element including a plurality of sensing pixel areas arranged in a matrix, wherein each of the sensing pixel areas includes a first pixel, a second pixel, a first shielding layer, a second shielding layer and at least one micro lens. The second pixel is adjacent to the first pixel in a predetermined direction. The first shielding layer is disposed upon the first pixel and has a first opening, wherein an aperture of the first opening increases along the predetermined direction from a center of the first pixel. The second shielding layer is disposed upon the second pixel and has a second opening, wherein a shape of the second opening is mirror symmetrical to that of the first opening along the predetermined direction. The at least one micro lens is disposed upon the first shielding layer and the second shield layer.

The present disclosure further provides an optical distance measurement system including a lens, a sensing element and a processing unit. The sensing element senses light penetrating the lens and outputs an image frame, and includes a plurality of sensing pixel areas arranged in a matrix, wherein each of the sensing pixel areas includes a first pixel, a second pixel, a third pixel, a fourth pixel, a first shielding layer, a second shielding layer, a third shielding layer, a fourth shielding layer and fourth micro lenses. The first shielding layer is disposed upon the first pixel and has a first opening, wherein an aperture of the first opening increases along a first direction from a center of the first pixel. The second shielding layer is disposed upon the second pixel and has a second opening, wherein a shape of the second opening is mirror symmetrical to that of the first opening along the first direction. The third shielding layer is disposed upon the third pixel and has a third opening, wherein an aperture of the third opening increases along a second direction from a center of the third pixel. The fourth shielding layer is disposed upon the fourth pixel and has a fourth opening, wherein a shape of the fourth opening is mirror symmetrical to that of the third opening along the second direction. The fourth micro lenses are respectively disposed between the lens and the first shielding layer, the second shielding layer, the third shielding layer as well as the fourth shielding layer. The processing unit generates, according to the image frame, a first subframe corresponding to the first pixels, a second subframe corresponding to the second pixels, a third subframe corresponding to the third pixels and a fourth subframe corresponding to the fourth pixels, and calculates at least two object distances according to the first subframe, the second subframe, the third subframe and the fourth subframe.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, advantages, and novel features of the present disclosure will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of an optical distance measurement system according to a first embodiment of the present disclosure.

FIG. 2A is a top view of a sensing element of the optical distance measurement system of FIG. 1.

FIG. 2B is a partially enlarged view of FIG. 2A.

FIG. 3 is a schematic diagram of a sensing element of an optical distance measurement system according to one embodiment of the present disclosure.

FIG. 4 is a schematic diagram of estimating an object distance according to an image frame by a processing unit according to a first embodiment of the present disclosure.

FIG. 5A is a top view of a sensing element of an optical distance measurement system according a second embodiment of the present disclosure.

FIG. 5B is a schematic diagram of estimating an object distance according to an image frame by a processing unit according to a second embodiment of the present disclosure.

FIGS. 6A-8B are schematic diagrams of sensing pixel areas having openings of different shapes.

FIG. 9 is a top view of a sensing element of an optical distance measurement system according a third embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENT

It should be noted that, wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Referring to FIG. 1, it is a schematic diagram of an optical distance measurement system 1 according to a first embodiment of the present disclosure. The optical distance measurement system 1 includes a lens 10, a sensing element 12 and a processing unit 14. In this embodiment, the optical distance measurement system 1 is used to estimate at least one object distance. For example, when an object 9 enters a valid detection range of the optical distance measurement system 1, the optical distance measurement system 1 estimates at least one distance of the object 9 with respect to the optical distance measurement system 1 (described later).

It should be mentioned that FIG. 1 shows only one object (e.g. the object 9) for illustrating the present disclosure, but not limited thereto. In some embodiments, the distance of each of a plurality of objects within the valid detection range of the optical distance measurement system 1 is able to be estimated. In some embodiments, the object 9 has a rough surface, and the optical distance measurement system 1 estimates a plurality of distances, with respect to the optical distance measurement system 1, of different positions on the rough surface of the object 9 to obtain three-dimensional image information.

The lens 10 is used to condense light, e.g., reflected light from the object 9. The lens 10 is separated, e.g., via a spacer, but not limited to, from the sensing element 12 by a fixed distance. In other embodiments, the lens 10 keeps the fixed distance from the sensing element 12 by a casing or a supporting member. In addition, although FIG. 1 shows one lens 10, the present disclosure is not limited thereto. In other embodiments, the lens 10 is a lens set including a plurality of lenses.

The sensing element 12 is used to capture light penetrating the lens 10 and output an image frame IF. The sensing element 12 is, e.g., a charge coupled device (CCD) image sensor, a complementary metal oxide semiconductor (CMOS) image sensor or other sensors for sensing light energy. The sensing element 12 includes a plurality of sensing pixel areas As arranged in a matrix, wherein each of the sensing pixel areas As includes a first pixel P₁, a second pixel P₂, a first shielding layer S₁, a second shielding layer S₂ and at least one micro lens L_(M).

Referring to FIGS. 1, 2A and 2B, every component of each of the sensing pixel areas As is illustrated hereinafter. FIG. 2A is a top view of the sensing element 12 of FIG. 1, wherein the at least one micro lens L_(M) is not shown in FIG. 2A. As shown in FIG. 2A, the second pixel P₂ is adjacent to the first pixel P₁ in a predetermined direction (e.g. an x direction) in this embodiment. In addition, in this embodiment, a shape of the first pixel P₁ and the second pixel P₂ is shown as a square, but not limited thereto. In other embodiments, a shape of the first pixel P₁ and the second pixel P₂ is a circle or a rectangle. Although FIG. 2A shows that the sensing element 12 has 6×5 sensing pixel areas As, but the present disclosure is not limited thereto. A number of the sensing pixel areas As is determined according to actual applications.

FIG. 2B is a partial enlarged view of FIG. 2A, and in FIG. 2B one sensing pixel area As is shown. The first shielding layer S₁ is disposed upon the first pixel P₁ and has a first opening O₁, wherein an aperture of the first opening O₁ increases or monotonically increases along the predetermined direction from a center of the first pixel P₁. The second shielding layer S₂ is disposed upon the second pixel P₂ and has a second opening O₂, wherein a shape of the second opening O₂ is mirror symmetrical to that of the first opening O₁ along the predetermined direction (e.g. the X direction). That is, an aperture of the second opening O₂ increases along an inverse direction of the predetermined direction from a center of the second pixel P₂. It should be mentioned that the first shielding layer S₁ and the second shielding layer S₂ are used to block a part of light penetrating the micro lens L_(M). The other part of light not being blocked propagates through the first opening O₁ of the first shielding layer S₁ and the second opening O₂ of the second shielding layer S₂ and reaches the first pixel P₁ and the second pixel P₂.

It is appreciated that, in FIG. 2B, a first area summation of the first shielding layer S₁ and the first opening O₁ is equal to an area of the first pixel P₁, and a second area summation of the second shielding layer S₂ and the second opening O₂ is equal to an area of the second pixel P₂, but not limited to. In other embodiments, the first area summation is a little larger than the area of the first pixel P₁ and the second area summation is a little larger than the area of the second pixel P₂ to avoid light leakage.

The first shielding layer S₁ and the second shielding layer S₂ are selected from two layers of the first metal layer to the tenth metal layer in the CMOS manufacturing process, or made of other light shielding material.

In one embodiment, after the first shielding layer S₁ and the second shielding layer S₂ are formed, e.g., made of metal material, an isolation layer or a passivation layer is optionally covered on the first shielding layer S₁ and the second shielding layer S₂. In this case, the isolation layer or the passivation layer is preferably made of light transmissive material such that the first opening 01 and the second opening O₂ have a high light transmission rate. It is appreciated that the isolation layer or the passivation layer is able to prevent dust from entering the first pixel P₁ and the second pixel P₂ to degrade the light sensitivity.

In this embodiment, although FIG. 1 shows that the first shielding layer S₁ and the second shielding layer S₂ are separated from the first pixel P₁ and the second pixel P₂ by a distance (e.g. via the isolation layer or the passivation layer), the first shielding layer S₁ and the second shielding layer S₂ are preferably close to the first pixel P₁ and the second pixel P₂ as much as possible. In other embodiments, the first shielding layer S₁ and the second shielding layer S₂ are directly coated on or laid over the first pixel P₁ and the second pixel P₂, respectively.

The at least one micro lens L_(M) is disposed between the lens 10 and the first shielding layer S₁ as well as the second shielding layer S₂. As shown in FIG. 1, for example each of the sensing pixel areas As includes two micro lenses L_(M), and the two micro lenses L_(M) are respectively aligned with the first pixel P₁ and the second pixel P₂. In this case, through the arrangement of the two micro lenses L_(M) as well as the first opening O₁ and the second opening O₂ being mirror symmetrical to each other, the first pixel P₁ and the second pixel P₂ respectively receive incident light beams of different phases for the phase detection.

It should be mentioned that through the above arrangement of the micro lens and the opening, when the first pixel P₁ and the second pixel P₂ receives incident light beams, received incident light closing to a center of the first pixel P₁ and received incident light closing to a center of the second pixel P₂ do not have an obvious phase difference from each other. On the contrary, received incident light closing to an edge (e.g. a right edge in FIG. 2B) of the first pixel P₁ and received incident light closing to an edge (e.g. a left edge in FIG. 2B) of the second pixel P₂ have a larger phase difference from each other. Therefore, corresponding to the first opening O₁, the aperture of the first opening O₁ closing to the edge of the first pixel P₁ is preferably larger than the aperture of the first opening O₁ closing to the center of the first pixel P₁. That is, the aperture of the first opening O₁ increases along the predetermined direction from the center of the first pixel P₁. In this way, the accuracy of phase detection is increased.

It is appreciated that as the aperture of the first opening O₁ increases along the predetermined direction from the center of the first pixel P₁, an area of the first opening O₁ is smaller than a half area of the first pixel P₁, as shown in FIG. 2B. Meanwhile, areas of the first opening O₁ and the second opening O₂ are larger than a predetermined area such that the image frame IF captured by the sensing element 12 has an acceptable signal to noise ratio (SNR). Preferably, an area of the first opening O₁ is 5 to 45 percent of an area of the first pixel P₁.

As the micro lens L_(M) has a symmetrical structure, in other embodiments each of the sensing pixel areas As includes only one micro lens L_(M). In this case, the one micro lens L_(M) is aligned with both of the first opening O₁ and the second opening O₂, as shown in FIG. 3. In addition, a passivation layer is optionally formed between the micro lenses L_(M) and the shielding layers.

Referring to FIGS. 1, 2A and 4, FIG. 4 is a schematic diagram of estimating an object distance according to an image frame IF by a processing unit 14. The processing unit 14 is, e.g., a digital signal processor (DSP) or a processing circuit, and electrically coupled to the sensing element 12. After the sensing element 12 outputs the image frame IF (e.g. corresponding to the 6×10 pixel matrix shown in FIG. 2A) to the processing unit 14, the processing unit 14 generates, according to the image frame IF, a first subframe F₁ corresponding to the first pixels P₁ and a second subframe F₂ corresponding to the second pixels P₂. For example, when the image frame IF corresponds to the 6×5 sensing pixel areas As of the sensing element 12 (i.e. the 6×10 pixel matrix) of FIG. 2A, gray level information of the 6×5 first pixels P₁ and the 6×5 second pixels P₂ are used to form the first subframe F₁ and the second subframe F₂, respectively.

Generally, when the object 9 is in focus with respect to the optical distance measurement system 1, a clear object image appears in the image frame IF captured by the sensing element 12. Meanwhile, corresponding imaging positions of the object 9 in the first subframe F₁ and in the second subframe F₂ generated according to the image frame IF are substantially identical. That is, when the imaging positions of the object 9 respectively present in the first subframe F₁ and the second subframe F₂ are overlapped (e.g. a distance therebetween is 0), a linear distance between the object 9 and the optical distance measurement system 1 is defined as a reference distance L0 herein.

However, when the object 9 is out of focus with respect to the optical distance measurement system 1, two object images are present in the image frame IF captured by the sensing element 12, and the two object images are at a first imaging position I₁ in the first subframe F₁ and at a second imaging position I₂ in the second subframe F₂, as shown in FIG. 4. In this case, for example a center line in the first subframe F₁ perpendicular to the predetermined direction is defined as a first reference line R₁ and for example a center line in the second subframe F₂ perpendicular to the predetermined direction is defined as a second reference line R₂. Then, the processing unit 14 calculates a first projective distance D₁ between the first imaging position I₁ and the first reference line R₁ and calculates a second projective distance D₂ between the second imaging position I₂ and the second reference line R₂.

It should be mentioned that the reference distance L0 is assumed to be known when the first imaging position I₁ and the second imaging position I₂ are overlapped, and in this case the first projective distance D₁ and the second projective distance D₂ are both 0 if the object image is at the center of the image frame IF. As a distance of the object 9 from the optical distance measurement system 1 has a predetermined relationship, e.g. a linear or nonlinear relationship, with respect to the first projective distance D₁ of the first imaging position I₁ generated by the object 9 in the first subframe F₁ (or the second projective distance D₂ of the second imaging position I₂ generated by the object 9 in the second subframe F₂), the optical distance measurement system 1 previously stores the reference distance L0 and the predetermined relationship in a storage memory. Accordingly, the processing unit 14 is able to estimate at least one object distance (i.e. the distance of the object 9 from the optical distance measurement system 1) according to the first imaging position I₁ and the second imaging position I₂.

In one embodiment, the processing unit 14 estimates the at least one object distance according to a difference value between the first projective distance D₁ and the second projective distance D₂ (e.g., D₁-D₂). For example, a look-up table, e.g. shown in Table 1 below (wherein the object distance L2>L0>L1), is previously formed according to a relationship of the difference value with respect to the distance of the object 9 from the optical distance measurement system 1 to be previously stored in the storage memory.

TABLE 1 first projective second projective difference value object distance D₁ distance D₂ (D₁ − D₂) distance 0 0 0 L0 −1 +1 −2 L1 +1 −1 2 L2

In another embodiment, the relationship of the difference value with respect to the distance between the object 9 and the optical distance measurement system 1 is formed as a linear equation mathematically to be previously stored in the storage memory, but not limited thereto. In brief, the processing unit 14 of the optical distance measurement system 1 of this embodiment calculates at least one object distance according to the first imaging position I₁ of the first subframe F₁ and the second imaging position I₂ of the second subframe F₂. Compared with the conventional distance measurement system (DMS) which requires lighting, the lighting is not necessary in the optical distance measurement system 1 of this embodiment and the object distance is detectable using a less number of first pixels P₁ and second pixels P₂ such that this embodiment has the advantages of low cost and small size.

Compared with the first embodiment of the present disclosure in which the sensing pixel area As includes two mirror symmetrical pixels (e.g. the first pixel P₁ and the second pixel P₂), the sensing pixel area As of the second embodiment of the present disclosure includes more than two pixels, e.g., including four pixels. Referring to FIGS. 1, 5A and 5B, FIG. 5A is a top view of a sensing element according a second embodiment of the present disclosure, and FIG. 5B is a schematic diagram of estimating an object distance according to an image frame by a processing unit according to a second embodiment of the present disclosure. An optical distance measurement system 1 of the second embodiment of the present disclosure includes a lens 10, a sensing element 12 and a processing unit 14, wherein the function of the lens 10 has been described in the first embodiment and thus details thereof are not repeated herein.

The sensing element 12 is used to sense light penetrating the lens 10 and output an image frame (e.g. an image frame IF shown in FIG. 5B, the image frame IF corresponding to a 8×12 pixel matrix of FIG. 5A). The sensing element 12 includes a plurality of sensing pixel areas As arranged in a matrix, wherein each of the sensing pixel areas As includes a first pixel P₁, a second pixel P₂, a third pixel P₃ and a fourth pixel P₄, as shown in FIG. 5A.

Each of the sensing pixel areas As further includes a first shielding layer S₁, a second shielding layer S₂, a third shielding layer S₃ and a fourth shielding layer S₄. The first shielding layer S₁ is disposed upon the first pixel P₁ and has a first opening O₁, wherein an aperture of the first opening O₁ increases or monotonically increases along a first direction (e.g. an x direction) from a center of the first pixel P₁. The second shielding layer S₂ is disposed upon the second pixel P₂ and has a second opening O₂, wherein a shape of the second opening O₂ is mirror symmetrical to that of the first opening O₁ in the first direction. The third shielding layer S₃ is disposed upon the third pixel P₃ and has a third opening O₃, wherein an aperture of the third opening O₃ increases or monotonically increases along a second direction (e.g. a y direction) from a center of the third pixel P₃. The fourth shielding layer S₄ is disposed upon the fourth pixel P₄ and has a fourth opening O₄, wherein a shape of the fourth opening O₄ is mirror symmetrical to that of the third opening O₃ in the second direction.

In this embodiment, the first direction (e.g. the x direction) is perpendicular to the second direction (e.g. the y direction), but not limited thereto.

Then, four micro lenses (not shown) are respectively disposed between the lens 10 and the first shielding layer S₁, the second shielding layer S₂, the third shielding layer S₃ as well as the fourth shielding layer S₄, e.g., respectively arranged upon the shielding layer S₁ to S₄ and aligned with the first pixel P₁, the second pixel P₂, the third pixel P₃ and the fourth pixel P₄, wherein the micro lenses in this embodiment have the same function as the micro lenses L_(M) of the first embodiment and thus details thereof are not repeated herein.

It should be mentioned that the first opening O₁ and the second opening O₂ of this embodiment respectively have identical shapes and functions to the first opening O₁ and the second opening O₂ of the first embodiment. However, different from the first embodiment, the sensing pixel area As of this embodiment further includes the third opening O₃, the fourth opening O₄ and corresponded pixels and shielding layers. It is appreciated that after the third shielding layer S₃ and the fourth layer S₄ are counterclockwise rotated about the sensing pixel area As by 90 degrees, the rotated third shielding layer S₃ and the rotated fourth shielding layer S₄ respectively have an identical shape to the first shielding layer S₁ and the second shielding layer S₂. Meanwhile, the rotated third opening O₃ and the rotated fourth opening O₄ respectively have an identical shape to the first opening O₁ and the second opening O₂. Accordingly, the third opening O₃ and the fourth opening O₄ have the same function, in the second direction, as the first opening O₁ and the second opening O₂ in the first direction.

Next, in addition to generating a first subframe F₁ corresponding to the first pixels P₁ and a second subframe F₂ corresponding to the second pixels P₂ according to the image frame IF, the processing unit 14 further generates a third subframe F₃ corresponding to the third pixels P₃ and a fourth subframe F₄ corresponding to the fourth pixels P₄ according to the image frame IF, and estimates at least two object distances according to a first imaging position I₁ of the first subframe F₁, a second imaging position I₂ of the second subframe F₂, a third imaging position I₃ of the third subframe F₃ and a fourth imaging position I₄ of the fourth subframe F₄.

For example, the first subframe F₁ and the second subframe F₂ respectively have a center line perpendicular to the first direction (e.g. the x direction) to be defined as a first reference line R₁ and a second reference line R₂, respectively. The third subframe F₃ and the fourth subframe F₄ respectively have a center line perpendicular to the second direction (e.g. the y direction) to be defined as a third reference line R₃ and a fourth reference line R₄, respectively. The processing unit 14 then calculates a first projective distance D₁ between the first imaging position I₁ and the first reference line R₁, calculates a second projective distance D₂ between the second imaging position I₂ and the second reference line R₂, calculates a third projective distance D₃ between the third imaging position I₃ and the third reference line R₃ and calculates a fourth projective distance D₄ between the fourth imaging position I₄ and the fourth reference line R₄, and estimates the at least two object distances according to a first difference value between the first projective distance D₁ and the second projective distance D₂ and according to a second difference value between the third projective distance D₃ and the fourth projective distance D₄, wherein the method of the processing unit 14 estimating the object distance has been described in the first embodiment and FIG. 4, and thus details thereof are not repeated herein.

In addition, as the third shielding layer S₃ and the first shielding layer S₁ of the sensing element 12 have an identical shape, a third opening O₃ of the third shielding layer S₃ has an identical shape and area as a first opening O1 of the first shielding layer S₁, e.g., a triangle shown in FIG. 5A, but not limited thereto. In one embodiment, the first opening O₁ and the third opening O₃ have an identical area but different shapes, e.g., the first opening O₁ being a trapezoid and the second opening O₂ being a semicircle, and the trapezoid and the semicircle have an identical area.

In the embodiment of the present disclosure, a shape of the opening included in the shielding layer of the sensing pixel areas does not have particular limitations as long as an aperture of the opening increases along a predetermined direction from a corresponded pixel center. For example in FIG. 6A, an aperture of the first opening O₁ exponentially increases along a first direction (e.g. the X direction) from a center of the first pixel P₁. It is appreciated that as the second opening O₂ is mirror symmetrical to the first opening O₁ along the first direction, an aperture of the second opening O₂ exponentially increases along an inverse of the first direction (e.g. the −X direction) from a center of the second pixel P₂. Furthermore, when the sensing pixel area includes four sensing pixels as shown in FIG. 6B, an aperture of the third opening O₃ exponentially increases along a second direction (e.g. the Y direction) from a center of the third pixel P₃, and an aperture of the fourth opening O₄ exponentially increases along an inverse of the second direction (e.g. the −Y direction) from a center of the fourth pixel P₄.

In one embodiment, a shape of the first opening O₁, the second opening O₂, the third opening O₃ and the fourth opening O₄ is a semicircle as shown in FIGS. 7A and 7B.

In one embodiment, a shape of the first opening O₁, the second opening O₂, the third opening O₃ and the fourth opening O₄ is a trapezoid as shown in FIGS. 8A and 8B.

In the present disclosure, each of the sensing pixel areas As (e.g. including the first pixel P₁, the second pixel P₂, the third pixel P₃ and the fourth pixel P₄) is the light sensing pixel manufactured independently or light sensing pixels adjacent or non adjacent to each other in a same pixel matrix without particular limitations. In some embodiments, a part of pixels in a pixel matrix are selected as the sensing pixel areas As and the other pixels of the pixel matrix perform other functions.

For example referring to FIG. 9, a sensing element includes three types of sensing pixels including red pixels (R), green pixels (G) and blue pixels (B) is shown. A part of the G pixels are respectively disposed with a shielding layer and a micro lens thereupon, wherein the shielding layer includes an opening (e.g. triangular first opening O₁ and second opening O₂ in the first embodiment of the present disclosure). The other part of the G pixels, the R pixels and the B pixels are not disposed with the shielding layer and the micro lens thereupon. In this case, the part of the G pixels are used to capture the image frame containing information of object depth, and the other pixels are used to capture the image frame containing information of two-dimensional image.

In addition, the optical distance measurement system 1 of the present disclosure is able to estimate the position of the object 9 using a few sensing pixels (e.g. the first pixel P₁ and the second pixel P₂). In other words, if the optical distance measurement system 1 of the present disclosure includes a large number of sensing pixels, e.g. a sensing pixel matrix including 300×300, 600×600 or 900×900 pixels, more position information of the object 9 is obtainable to be used to construct a three dimensional image of the object 9.

It should be mentioned that values in the above embodiments, e.g. the projective distances and different values, are only intended to illustrate but not to limit the present disclosure.

As mentioned above, the conventional distance measurement system and the gesture recognition system need a higher cost and size, and generally an additional light source is required. Therefore, the present disclosure provides a sensing element and an optical distance measurement system (FIG. 1) that capture images with mirror symmetrical sensing pixels to perform the phase detection so as to identify the two-dimensional position, the three-dimensional position and the position variation of an object, and have the advantages of low cost and small size since a light source is not required.

Although the disclosure has been explained in relation to its preferred embodiment, it is not used to limit the disclosure. It is to be understood that many other possible modifications and variations can be made by those skilled in the art without departing from the spirit and scope of the disclosure as hereinafter claimed. 

What is claimed is:
 1. An optical distance measurement system comprising: a lens; a sensing element configured to sense light penetrating the lens and output an image frame, and comprising a plurality of sensing pixel areas arranged in a matrix, wherein each of the sensing pixel areas comprising: a first pixel; a second pixel adjacent to the first pixel in a predetermined direction; a first shielding layer disposed upon the first pixel and having a first opening, wherein an aperture of the first opening increases along the predetermined direction from a center of the first pixel; a second shielding layer disposed upon the second pixel and having a second opening, wherein a shape of the second opening is mirror symmetrical to that of the first opening along the predetermined direction; and at least one micro lens disposed between the lens and the first shielding layer as well as the second shielding layer; and a processing unit configured to generate, according to the image frame, a first subframe corresponding to the first pixels and a second subframe corresponding to the second pixels, and calculate at least one object distance according to the first subframe and the second subframe.
 2. The optical distance measurement system as claimed in claim 1, wherein each of the sensing pixel areas comprises one micro lens which is aligned with both of the first opening and the second opening.
 3. The optical distance measurement system as claimed in claim 1, wherein each of the sensing pixel areas comprises two micro lenses each being aligned with one of the first opening and the second opening.
 4. The optical distance measurement system as claimed in claim 1, wherein the first shielding layer and the second shielding layer are respectively coated on or laid over the first pixel and the second pixel.
 5. The optical distance measurement system as claimed in claim 1, wherein an area of the first opening is 5 to 45 percent of that of the first pixel.
 6. The optical distance measurement system as claimed in claim 1, wherein a shape of the first opening and the second opening is a triangle, a trapezoid or a semicircle.
 7. The optical distance measurement system as claimed in claim 1, wherein the aperture of the first opening exponentially increases along the predetermined direction from the center of the first pixel.
 8. The optical distance measurement system as claimed in claim 1, wherein the processing unit is further configured to calculate a first projective distance from a first imaging position to a first reference line in the first subframe, calculate a second projective distance from a second imaging position to a second reference line in the second subframe, and estimate the at least one object distance according to a difference value of the first projective distance and the second projective distance.
 9. The optical distance measurement system as claimed in claim 8, further comprising: a storage memory configured to store a predetermined relationship between the difference value with respect to the object distance.
 10. A sensing element comprising: a plurality of sensing pixel areas arranged in a matrix, wherein each of the sensing pixel areas comprises: a first pixel; a second pixel adjacent to the first pixel in a predetermined direction; a first shielding layer disposed upon the first pixel and having a first opening, wherein an aperture of the first opening increases along the predetermined direction from a center of the first pixel; a second shielding layer disposed upon the second pixel and having a second opening, wherein a shape of the second opening is mirror symmetrical to that of the first opening along the predetermined direction; and at least one micro lens disposed upon the first shielding layer and the second shield layer.
 11. The sensing element as claimed in claim 10, wherein the first shielding layer and the second shielding layer are respectively coated on or laid over the first pixel and the second pixel.
 12. The sensing element as claimed in claim 10, wherein an area of the first opening is 5 to 45 percent of that of the first pixel.
 13. The sensing element as claimed in claim 10, wherein a shape of the first opening and the second opening is a triangle, a trapezoid or a semicircle.
 14. The sensing element as claimed in claim 10, wherein the aperture of the first opening exponentially increases along the predetermined direction from the center of the first pixel.
 15. An optical distance measurement system comprising: a lens; a sensing element configured to sense light penetrating the lens and output an image frame, and comprising a plurality of sensing pixel areas arranged in a matrix, wherein each of the sensing pixel areas comprising: a first pixel, a second pixel, a third pixel and a fourth pixel; a first shielding layer disposed upon the first pixel and having a first opening, wherein an aperture of the first opening increases along a first direction from a center of the first pixel; a second shielding layer disposed upon the second pixel and having a second opening, wherein a shape of the second opening is mirror symmetrical to that of the first opening along the first direction; a third shielding layer disposed upon the third pixel and having a third opening, wherein an aperture of the third opening increases along a second direction from a center of the third pixel; a fourth shielding layer disposed upon the fourth pixel and having a fourth opening, wherein a shape of the fourth opening is mirror symmetrical to that of the third opening along the second direction; and fourth micro lenses respectively disposed between the lens and the first shielding layer, the second shielding layer, the third shielding layer as well as the fourth shielding layer; and a processing unit configured to generate, according to the image frame, a first subframe corresponding to the first pixels, a second subframe corresponding to the second pixels, a third subframe corresponding to the third pixels and a fourth subframe corresponding to the fourth pixels, and calculate at least two object distances according to the first subframe, the second subframe, the third subframe and the fourth subframe.
 16. The optical distance measurement system as claimed in claim 15, wherein the first opening and the third opening have an identical shape or an identical area.
 17. The optical distance measurement system as claimed in claim 15, wherein a shape of the first opening and the third opening is a triangle, a trapezoid or a semicircle.
 18. The optical distance measurement system as claimed in claim 15, wherein the aperture of the first opening exponentially increases along the first direction from the center of the first pixel, and the aperture of the third opening exponentially increases along the second direction from the center of the third pixel.
 19. The optical distance measurement system as claimed in claim 15, wherein the processing unit is further configured to calculate a first projective distance from a first imaging position to a first reference line in the first subframe, calculate a second projective distance from a second imaging position to a second reference line in the second subframe, calculate a third projective distance from a third imaging position to a third reference line in the third subframe, calculate a fourth projective distance from a fourth imaging position to a fourth reference line in the fourth subframe, and estimate the at least two object distances according to a first difference value of the first projective distance and the second projective distance and according to a second difference value of the third projective distance and the fourth projective distance.
 20. The optical distance measurement system as claimed in claim 15, wherein the first direction is perpendicular to the second direction. 